The present invention relates generally to magnetometers, and more particularly, to a digital flux gate magnetometer.
The assignee of the present invention uses data from three axis flux gate magnetometers for its magnetic data processing systems such as those described in U.S. Pat. No. 5,239,474, and U.S. patent application Ser. No. 08/611,352, filed Mar. 5, 1996. The present state of the art employs an analog magnetic flux gate sensor and uses the output of an analog integrator as the magnetometer output. This signal is then digitized with an analog to digital converter having a large number of bits of resolution (typically &gt;20). This requires the use of large, expensive, and power hungry analog to digital converters that presently have a dynamic range that is limited to around 22 bits of resolution. The analog integrator used in the analog flux gate sensor causes drift in the output signal of the sensor. The output of the analog flux gate sensor varies with temperature due to the non-constant resistance of the core windings with temperature.
A stopgap measure presently being utilized to get around the use of the expensive analog to digital converter is to employ an adjustable voltage reference and an analog subtractor to subtract the large constant part of the measured magnetic field due to the earth's magnetic field. Then, the remaining signal is digitized with a reduced resolution analog to digital converter (12 to 16 bits). This technique only works for applications in which the sensor is stationary with respect to the earth's magnetic field.
Alternatively, prior art magnetometers have used a very low frequency high pass filter to remove the constant component of the local field and then the remaining signal is digitized by an analog to digital converter. The prior art systems have the following drawbacks: They exhibit loss of absolute magnetic field values (which are useful for determining the heading of the sensor). They exhibit distortion (due to the high pass filtering) of the low frequency wave forms. Such distortion adversely impacts the performance the magnetic processing algorithms. They exhibit susceptibility to overload if the sensor is used in an application in which it is moved with respect to the ambient magnetic field.
Accordingly, it is an objective of the present invention to provide for a digital flux gate magnetometer that overcomes the limitations of conventional magnetometers.